The hypothesis that d-tubocurarine injected intravenously blocks synaptic transmission by a direct action in the cerebral cortex was examined. Injections of 3 mg/kg d-tubocurarine caused either no fall, moderate decreases, or complete obliteration of direct cortical responses (DCR's) with little return to control levels within 30–60 minutes. Blood pressure was recorded and drops to 50–60 mm Hg or below were associated with moderate to severe decreases of DCR's; drops below 40 mm Hg with elimination of the DCR. Diminishing the blood pressure to 50–60 mm Hg by bleeding resulted in moderately to greatly decreased DCR's. Bleedings to a pressure of 35–40 mm Hg might give rise to an ‘enhancing effect’ before DCR's were completely diminished. During enhancement DCR's became several times larger than control height. This effect was interpreted as a differential loss of an inhibitory component. Decrease of DCR's after injecting d-tubocurarine is considered secondary to the lower blood pressure.
NIH study results support lower blood pressure target with drugs
